Protons and neutrons
Explanation:
According to the accepted theory of the structure of an atom ( note it isn't 100% accurate) the center of the atom, or the nucleus, contains the protons and neutrons. Around the nucleus you have electrons, which are located in electron shells and orbit the nucleus in nearly circular elliptical orbits. They orbit the nucleus because they are attracted to the protons in the nucleus (opposite charged particles attract one another.)